SESSION: Ideal for OLTP systems where transactions are small. In case of failover, a new session is automatically created for the user on the backup node.

SELECT: If the connection is lost, Oracle Net establishes a connection to another node and re-executes the SELECT statements with cursor positioned on the row on which it was positioned prior to the failover. This mode involves overhead on the client side and Oracle NET keeps track of SELECT statements. This approach is best for data warehouse systems, where the transactions are big and complex.